1. Field of the Invention
The present invention relates to an electromagnetic ultrasonic flaw detection method for inspecting a fin-implanted heat transfer tube of an air cooling heat exchanger for detection of corrosion, and an electromagnetic ultrasonic transducer to be used for the method.
2. Description of the Related Art
If an interior surface of a finned heat transfer tube of an air cooling heat exchanger is corroded to a greater extent, a fluid flowing through the tube is liable to leak out of the tube. Therefore, the interior surface of the finned heat transfer tube is inspected for detection of corrosion.
Examples of a conventional inspection method for detecting the corrosion of the interior surface of the finned heat transfer tube include an eddy current flaw detection method which utilizes an AC magnetic flux generated by a coil provided in a probe for flaw detection (see, for example, Japanese Unexamined Patent Publication No. JP-A1-2002-296241), and an ultrasonic flaw detection method which utilizes ultrasonic waves generated by oscillating an oscillator for flaw detection (see, for example, Japanese Unexamined Patent Publication No. JP-A1-2001-50936).
Where the tube has fins, however, the eddy current flaw detection method fails to detect the corrosion of the interior surface of the tube with high accuracy due to obstruction by the fins. This makes it impossible to employ the eddy current flaw detection method for the detection of the corrosion of the interior surface of the finned heat transfer tube. On the other hand, the ultrasonic flaw detection method requires greater time for inspection of a single heat transfer tube, making it impossible to perform 100% inspection in a short period of time because of its lower inspection speed. In addition, the heat transfer tube should be filled with water for the inspection, so that a post treatment such as dehydration should be performed. In some cases, the water cannot be used depending on the type of the fluid passing through the heat transfer tube. Further, the interior surface of the heat transfer tube should be scaled for increasing the inspection accuracy. Therefore, time and costs are required for the scaling and other pretreatments.
In view of the foregoing, it is an object of the present invention to provide an electromagnetic ultrasonic flaw detection method which ensures highly accurate inspection of an interior surface of a fin-implanted heat transfer tube for detection of corrosion, and requires less time for the inspection, no contact medium such as water, and less time and less costs for a pretreatment, and to provide an electromagnetic ultrasonic transducer to be used for the method.